The present invention relates to the art of packaging integrated circuit chips. More particularly, the present invention relates to improved packages for hermetically securing integrated circuit chips with high pin counts to an isolated environment.
Integrated circuit packages comprise an integrated circuit chip that has been encapsulated in a protective material such as plastic or ceramic. These packages can be with or without leads. In the former, electrical conductors extend from the encapsulant as a means for sending signals to and receiving signals from the chip; whereas in the latter, communication with the chip is accomplished by electrical pads that lie flush with the encapsulant.
The manufacturing technique of the pin grid array packages available nowadays involves the use of either plastics or ceramics. In the case of plastic material, poor heat transfer renders it inappropriate for use under high temperatures and high power applications. Also, it does not possess a desired hermiticity and humidity-resistance. With the substrate of plastic material in contact with the gold line and IC chip, different thermal expansion factors therebetween result in poor resistance to temperature cycling. In the case of ceramic material, the manufacturing is a co-fire process which combines alumina or other suitable material and binder to form the slip and then the green tape. Next, desired circuitry is screened on the green tape which in turn is punched to make connections for several layers of green tapes. The several layers of green tapes are laminated together and heat treated under reduced atmosphere. Next, the pins are fixed in position by copper/silver brazing and metal is plated thereon. After die bonding and wire bonding, a kovar cover with gold/tin preform is soldered to the gold plated seal ring on top of the ceramic package, at about 310 degrees Celsius.
The above process for ceramic material has the following shortcomings:
(1) Mg-Mo alloy or W, which is used for the desired circuitry in the co-fire process, has high ohmic resistance which reduces the signal transmission speed and cannot meet the high-speed signal processing requirements of today.
(2) Conventional co-fire process is performed under reduced atmosphere in a nitrogen/hydrogen environment which demands high cost.
(3) Co-fire substrates are formed with green tapes using binders of the solvent type which are expensive and liable to pollute the environment.
(4) Molds used for punching connection between the different layers are expensive to manufacture and difficult to modify.
It is the purpose of this present invention, therefore, to overcome the above drawbacks and to provide an improved pin grid array (package) in the manner set forth in the following detailed description.